3.7 Inheritance and populations

Question 1

What is monohybrid inheritance?

Answer 1

When a phenotype or characteristic is controlled by a single gene

Question 2

How is monohybrid usually coded in genetic diagrams ?

Answer 2

Single letter can be wither capital or lowercase. B, b

Question 3

What ratio is typically expected in a monohybrid cross for genetic crossing of two heterozygous parents ?

Answer 3

3:1

Question 4

Suggest two reasons why observed ratios are often not the same as expected ratios

Answer 4

1- Fertilisation is random
2- Fusion of gametes is random

Question 5

What is dihybrid inheritance ?

Answer 5

Characteristics controlled by two genes

Question 6

If two heterozygous parents for both genes are crossed in a dihybrid cross what ratio will you always get ?

Answer 6

9:3:3:1

Question 7

When a homozygous dominant parent is crossed with a homozygous recessive parent what is the percentage of the outcome?

Answer 7

100% heterozygous as both dominant alleles from one parent and both recessive alleles from the other parent

Question 8

What does F1 stand for ?

Answer 8

First generation

Question 9

A ratio of 9:3:3:1 would be expected in a dihybrid cross for two heterozygous parents unless…?

Answer 9

1- Crossing over occurs during meiosis
2- There is autosomal linkage

Question 10

What is autosomal linkage ? And what does it mean in terms of dihybrid inheritance?

Answer 10

When two genes are located on the same chromosome.
This means that the alleles for each gene linked on the same chromosome will be inherited together.

Question 11

What is codominance?

Answer 11

When both alleles are expressed in the phenotype

Question 12

How is codominance usually coded?

Answer 12

Gene^ Allele

Question 13

Give an example of how codominance is coded

Answer 13

C^R C^W

Question 14

What would the gametes be for a codominant C^R C^W

Answer 14

C^R and C^W

Question 15

What is meant by multiple alleles?

Answer 15

When a trait has 3 or more alleles. A common example is blood type

Question 16

What do dihybrid crosses show ?

Answer 16

How two genes are linked

Question 16

Why is blood type an example of co dominance ?

Answer 16

As it has 3 different alleles that can produce 4 different blood groups

Question 17

What is sex linkage ?

Answer 17

A gene who’s locus is on the X chromosome

Question 17

How is sex linkage usually coded ?

Answer 17

Chromosome^ allele

Question 17

Give an example of how sex linkage is coded

Answer 17

X^R X^r OR X^RY

Question 17

Why is haemophilia a sex linked disease?

Answer 17

As it can only be carried on the X chromosome

Question 18

What is autosomal linkage ?

Answer 18

Genes that are located on the same chromosome

Question 19

How is autosomal linkage usually coded ?

Answer 19

With a single letter and can be capital or Lower case

Question 20

Give an example of autosomal linkage coding

Answer 20

Aa OR Bb

Question 21

What are autosomes ?

Answer 21

Chromosomes which are not compared with sex determination

Question 22

What is epistasis ?

Answer 22

When one gene influences or masks the expression of another gene

Question 23

How is epistasis usually coded ?

Answer 23

Single letter either capital or lower case, Aa

Question 24

What are the two types of epistasis ?

Answer 24

Dominant and recessive

Question 25

What is dominant epistasis ? What ratio does it usually give

Answer 25

When the dominant allele at the first locus completely masks the allele at the second locus, usually gives the ratio 12:3:1

Question 26

What is recessive epistasis? What ratio does it usually give

Answer 26

When a recessive allele prevents the expression of another allele at the second locus. usually gives the ratio 9:3:4